Calcium-vanadium series ferrimagnetic garnets

ABSTRACT

Calcium-vanadium ferrimagnetic garnets having the compositions expressed by the formula:  Ca3-y Yy [Fe2] (Fe1.5-0.5x+0.5yGExV1.5-0.5x-0.5y)012, wherein values of x and y lie within the polygonal area A-B-C-D-E shown in FIG. 7 of the drawing which is bounded by the lines connecting the coordinates:

United States Patent Takamizawa et al. 1 Feb. 1, 1972 54 CALClUM-VANADIUM SERIES 3,268,452 8/1966 Geller ..2s2/62.s7 x FERRIMAGNETIC GARNETS 3,281,363 10/1966 Geller et al. ..252/62.59 x 3.291.740 12/1966 Espinosa ct ill. ..252/62.57 x

I-lldeo Takamizawa; Keilchi Yotsuyanagl; Takashl Okada, all of Tokyo. Japan Nippon Electric Company Limited, Tokyo, Japan Filed: Feb. 4, 1970 Appl. No.: 8,491

[72] lnventors:

[73] Assignee:

Foreign Application Priority Data US. Cl ..'...252/62.57,

Int. Cl ..Cl)4b 3/2 6; C64b 33710 References Cited UNITED STATES PATENTS 3,156,651 11/1964 Geller ..252/62.59X

Primary ExaminerTobias E. Levow Assistant Examiner.l. Cooper Attorney-Sandoe, Hopgood and Calimafde [57] ABSTRACT Calcium-vanadium ferrimagnetic garnets having the compositions expressed by the formula:

{C 3u 1 2] 1.50.5 +0.5u 1rV1. 5-0.5 x 0.5 12 0 wherein values of x and y lie within the polygonal area A-B-C-D-E shown in FIG. 7 of the drawing which is bounded by the lines connecting the coordinates:

X y A 0.05 0.05 B 0.8 0.05 C 1 .8 1 .1 D 0.5 2.4 E 0.05 2.4

and wherein the range expressed by the relation 0.95 y z E 1.05 is excluded from said area.

3 Claims, 13 Drawing Figures 4rrMs sum 1 OF 6 TEMPERA runs (c) 0 0.5 [a /.'s in INVENTORS moso TAKAMIZA WA BY KEIICHI YOTSUYANAGI G 2 rmasm 0x404 J wW M PMENIEMEB I 872 FIG-5 A 77' ORNE YS' PATENTEDFEB new 3.639.241

SHEET 8 OF 6 INVENTORS H/DEO TAKAMIZAWA KEIICHI YOTSUYANAGI BY TAKASHI OKADA FIG. I3

A T TORNEYS CALClUM-VANADIUM SERIES FERRIMAGNETIC GARNETS The present invention relates to calcium-vanadium (Ca- V) series ferrimagnetic garnets for use in microwave circuit elements operating in theVHF, UHF or SHF'band range. Among the required characteristics of magnetic materials for use in such microwave circuit elements are low magnetic losses and small temperature variations of the saturation magnetization values (41rMs). Desired values of 41rMs will vary according to the application of the magnetic materials. The essential condition for reducing the magnetic loss is that the ferromagnetic resonance linewidth (AH) be as low as possible. It has been known that the higher the Curie temperature, the lower becomes the temperature variation of the saturation magnetization (41'rMs) and that in order to lower the value of the linewidth (AH), which is subject to change with the sintering density and the presence or absence of a second phase, the sintering densities-must be made sufficiently large and there should be no second phase formation. The yttrium-iron series garnets (YIG) that have been most commonly used as magnetic materials in microwave applications offer the advantages of lower 4 1rMs values, higher Curie temperatures and lower magnetic losses than conventional spinel-type ferrites such as nickel series ferrites or magnesium-manganese series ferrites. These advantages of the yttrium-iron series garnets are considerably offset by defects such as the necessity for the use of yttrium oxide which is an expensive raw material and the need for sintering at extremely high temperatures and for long time intervals which are not suited for large-scale industrial production. Yttrium-iron garnets substituted with A1 for lowering the saturation magnetization have an other defect of a rapid lowering of the Curie temperature which inevitably causes a large variation of 411Ms with a temperature variation. On the other hand, magnesium-manganese series ferrites have defects such as iow Curie temperatures and the concomitant unfavorable temperature stability of the saturation magnetization. Therefore, the object of the present invention is to eliminate these defects and to provide microwave circuit element materials for use in the VHF, UHF or SHF band range, having excellent characteristics such as low 41rMs values of less than 800 gauss, low ferromagnetic resonance linewidth values, and high Curie temperatures.

The garnet compositions are generally expressed by a normal formula unit {A }[B ](C;,)O, wherein brackets{ and represent respectively the 240, I60 and 24a sites and A, B and C denote atoms occupying the respective sites. Fe has a preference for the two different sublattice sites (the 16a and the 24d sites) and the FeFe superinteractions in each of and between these sublattice sites cause the Fe magnetic moments at the 16a and 24d sites to be coupled antiferromagnetically. Under the situation of the relative site unbalance, wherein the magnetic moment at the 24d site is not equal to that at the 16a site, the garnet compositions manifest ferrimagnetism. It has been generally considered that the compositions manifest antiferromagnetism in case of the site balance and at which an abnormal phenomenon of AH occurs.

The value of 41rMs is determined by the relative site unbalance in the magnetic moment between the 16a and 24d sites for which Fe has a strong preference, while the temperature variation of 41rMs changes with the numbers of iron ions located on each sublattice site, kinds of nonmagnetic ions replacing the iron ions, and kinds of ions located on the 24c site.

The conventional calcium-vanadium garnet which can be expressed by a normal formula unit {Ca }[Fe ](Fe,, V, )0, was of little or no utility in that its AH values were in excess of 300 oersteds in spite of its advantage of possessing a high Curie temperature and low 41rMs values. It has been found possible in accordance with the instant invention to lower the values of AH by various substitutions in the calcium-vanadium garnet composition while preserving its'above-mentioned advantages and also to prepare magnetic materials having cluu'ncteristics superior to the conventional Ca-V garnet nuilcrial According to this invention, excellent magnetic materials for use in VHF, UHF or SHF band range, featuring sufficiently low AH values, high Curie temperatures, 41rMs values controllable'within suitable ranges, small temperature variations in the value of 4rrMs low manufacturing costs are obtained by the substitution of ions located on the 240 and 24d sites in Ca-V garnets with yttrium (Y) and germanium (Ge) ions and by the further substitution of ions on the 16a site with tantalum (Ta) ions.

The Ca-V garnet compositions substituted with Y and Ge of this invention are expressed by the chemical formula:

n -u l/ii sii l.s on.um hi.s-0.n.r-o.m |2 in which the values of x and y are required to lie within the polygonal area bounded by the lines connecting the co ordinates:

X Y 0.05 0.05 0.8 0.05 L8 l.l 0.5 2.4 0.05 2.4

on the x-y rectangular coordinates plane. Where the difference between the numbers of Fe ions located on the 16a site and the 24d site is 0.025 or less, an abnormal phenomenon of AH is observed and the values of AH cannot be improved. Of course, ferrimagnetism disappears if the difference is zero. Thus, the range of |2(l.50.5x+0.5y)| 5 0.025, i.e.,0.95 a y-x 1.05, should be excluded from the above-mentioned effective range for x and y of the Y-and Ge-substituted CaV garnet compositions of this invention.

According to this invention, the Y-and Ge-substituted Ca-V garnets can be further substituted with Ta. The garnet compositions thus obtained can be expresses as i a-u ui[ z-: zi( i.s-n.s:+o.su: z as-asx-osw-z) i2, in which x, y and z should be within the ranges 0.05 E x; 0.8, 0.05 g y E 1.4 and 0 z 0.17, and preferably the ranges 0.1-5x; 0.8, 0.05 g y 5 L4 and 0.02 g z 5 0.l7, respectively. Where the difference of the numbers of Fe ions between 16a and 24d sites |(2-z)-(1.50.5x+0.5y+z)| is 0.025 of less, the abnormal phenomenon of AH is observed, as mentioned previously. Accordingly, the compositions satisfying the relation 0.95 g 4z+y-x 5 1.05 should be excluded. Furthermoreit is. preferable ,to'exclude awider range of compositions in-which the difference is 0.1 or less, that is 0.8 4z+yx 1.2, in view of the effect on the improve n AHL V.

Both of the garnet compositions of this invention may be produced by presintering a mixture of oxides of the elements to be contained in the final product or a mixture of other compounds of such elements, which are easily decomposed into the respective oxides at elevated temperature, at a tempera ture or temperatures within the range of 800 to 1,150 C. for l to 8 hours in an oxidizing atmosphere, crushing and pressmolding it, followed by sintering the molded body at a temperature or temperatures within the range of 1,160" to l,3 50" C. for l to 30 hours in an oxidizing atmosphere.

Now a more detailed description and examples of this invention will be described by reference to the accompanying drawings, in which FIG. l is a graph of the 41rMs versus temperature characteristics of the garnet compositions of the prior art and of this invention which illustrates the advantages of this invention;

FIGS. 2 and 3 show, respectively, ferromagnetic resonance linewidths (AH) and Curie temperatures as a function of x for the Y-and Ge-Substituted Ca-V ferrimagnetic garnets of this invention with the compositions expressed as FIGS. 4, 5 and 6 show, respectively, Curie temperatures,

. ferromagnetic resonance linewidths (AH) and saturation magnetizations (4rrMs) as a function of y for the same compositions as in FIGS. 2 and 3;

FIG. 7 is a composition diagram illustrating the effective range hounded by the lines connecting the coordinates expressed by (x,y) within which the Y-and Ge-Substituted Ca-V series ferrimagnetic garnet compositions according to this in vention fall and the points of the coordinates (1, for typical garnet compositions listed in table 2;

the amounts of substitution and other parameters. The defect of sample No. 1]] can be also improved by further substituting Ca-ions with Y-ions in addition to the Geand Tat-substitutions as shown in the sample No. V composition. This garnet FIGS. 8 and 9 are graphs respectively illustrating the incomposition possesses a lower 4bMs and a lower AH value fluence of 2 (T 0n AH and 41I'MS the compositions (AH 76 the Y, Geand Ta-substitutions have succeeded pressed as in raising the Curie temperature which was lowered by the 3U tI 2z z]( 1.50.5.t+0.5|!+z x l.50.5.r0.5u-z) l2 Geand Ta-substitutions in the composition of sample No. where x=0.4 and y=0.4; lIl. Thus it has become possible to provide a composition H08. 10 and 11 are graphs illustrating the influence of x having both a high Curie temperature and an excellent (Ge) on AH and 41-rMs for the same compositions where y=0.4 41rMS versus temperature charactersitics as indicated in and z=0.l,respectively;and FIG. 1. In such a manner, magnetic materials can be pre- FIGS. 12 and 13 are graphs illustrating the influence of y pared, which possess low 47rMS. low AH. high Curie temp- (Y) on AH and 41rMs for the same compositions where x=0.4, I 5 eratures, and improved 41rMS versus temperature characz=0.l and F0.6,z=0.l,respectively. teristics, by substituting Ca-V garnets with Y and Ge or Referring first to FIG. 1 and table 1, the effects of the Gewith T Y d ig; M. and Y-Substitutions and Ge-, Y-, and Ta-substitutions on the Now examples and the effective range of the Y- and Ge-sub- Ca-V garnets will be outlined. stituted Ca-V garnet compositions will be described with Starting materials CaCO l e- 0 V 0 Ta,O 660,, and reference to FIGS. 2through 7.

Y O in such amounts were weighed, 350 grams in total in In preparing the samples, starting materials CaCO,, Fe,0;, each case, so that each of the compositions shown in table 1 V 0 GeO,, and Y,O;, each in varying amounts in the commay be finally obtained. These materials were admixed in a positions: I

ball mill made of steel, presintered at 900 C. for 4 hours, {Ca;, ,,Y,,}[Fe ](Fe, ,(ie,V, ,,)O compressed into the desired shapes, and then sintered at were weighed, admixed in a ball mill made of steel, presinl2l0 C. for 20 hours in air. The sintered products were tered at 900 C. for 4 hours, compressed into desired shapes, removed from the furnace when the furnace temperature followed by a sintering process at 1,260" C. in air for 15 hours. cooled down to 300 C. Then the values of the saturation mag- The sintered bodies were removed from the furnace when the netization (41rMs) at room temperature (2325 C.), the furnace temperature cooled down to 300 C. Thenmeasurelinewidth (AH) at 9 GHz., and the Curie temperature were ments of saturation magnetization (41rMs) at room temperameasured. ture (2325 C.), linewidth (AH) at 9.5 GHz. and Curie tem- Table 1 lists the results of measurements for the unsubperature were conducted. stituted, tantalum-substituted, tantalum-and germanium-sub- Referring to FIG. 2 illustrating the measurement result, it stituted, yttrium and germanium-substituted and tantalum-, will be seen that linewidth (AH) decreases with increasing x germanium-, and yttrium-substituted Ca-V series garnet comfor y=0 as indicated by curve a. Curve b is for y=0.5 and a positions to demonstrate the successively promoted substituas in AH als urs with increasing x. Curve c is for tion effects, as regards a decrease in the linewidth AH and an y= l -1 n i h H r a hes the compensation point at x=0;l increase in the Curie temperature. Q I I i v I I TABLE 1 Curie tern- AH pera- 41r Ms (oerture Composition (gauss) steds) C.)

Sample No:

I {Carl [Fez] (Fer ,5Vr .5)Orz 520 370 233 lC al [Fei.iTa.1l (FGLOVLOOIZ 310 170 205 i 81) m uJl l.4 eo.l l.2)012 580 8 16 .s. {C82.uYo.4l [F62] (F81 .eG6u.4Vr .u)0r2 80 143 218 V .4 {CHZJYUA} [F61 .aTarm] (F01.GG90.4V1.0)012 6 76 0 Measured 41rMs values as a function of the temperature of and, at this point it manifests an abnormal phenomenon. but the samples Nos. 1 through V contained in table 1 and also of even a for curves a and b, AH decreases with increasing 1:. As l min mr illustrated n HQ is clearly seen, an increase in x-that is, large substitutions of Sample of the unsubstituted Gil-V garnet P 6e0 is very effective in lowering the values of the linewidth tion, has no practical utilization in that its linewidth AH is as (AH). high as 370 with a resulting large magnetic loss, although it As shown in FIG. 3, however, an increase inx causes a P05585565 310W 41TM5 Value and a high Curie temperature decrease in the Curie temperature. Curves a, b, and 0 show The effectiveness Of tantalum-substitution in the sample N0. respectively Curie temperatures as a function of x for y=(), ll composition can be understood from a decrease in 41rMs y==0,5, and y==l.l. A rapid decrease in the Curie temperature caused by the substitution of Fe ion on the l6a site with Ta an be observed in the curve a-that is, the Curie temperature and at the same time, a decrease in AH, to a value of AH=l70, f 107 C. at x=0.8 drops to lower than 100 C. for an x value less than one-half of that of the unsubstituted Ca-V garnet. A in ex ess of 0.8. The materials having y=0 and x exceeding 0.8 further decrease in h value f to a value f is are of little utility in that the temperature stability of 41rMs is achieved by a further substitution of Fe ion on the 24d site eedingly low, When the substitution quantity of Y,o,, or with Ge as indicated in the sample No. [I] composition. This 5 the value of y, is increased under these circumstances, the value is less than one-fourth of the value of AH of sample No. I C ri temperature becomes lower than C. only after the composition and is one-half of the value of AH of sample No. point x=l .2 has been exceeded in the case of curve b or y=0.5, ll composition. A defect of the Taand Ge-substitution, howwhile in case of curve c, or =l.l, the Curie temperature ever, is a remarkable decrease in the Curie temperatur remains higher than 100 C. down to the pointx=l.8. In such a which in turn causes an increase in the temperature variation 70 way, increasing the value of y causes higher Curie tempera- Of tures and a more gradual decrease in the slope of the plot of This defect can be improved by substituting some fraction Curie temperature versus x. Stated more particularly, the of Ca-ions on the 240 site with Y-ions instead of by Ta-subdecrease in the Curie temperature due to an increase in x from stitution as shown in sample No. IV. This composition has a 0 to 1.0 in curves a (y=0), b (y=0.5), and c (y=l.l is respechigher Curie temperature. Though AH is increased in com- 75 tively 118, and 88 Centigrade. This indicates clearly parison with sample No. [I], it is possible to have a lower AH value with a sufiiciently high Curie temperature by changing that the rate of decrease of the Curie temperature becomes smaller with increasing y.

To demonstrate the effect of this invention for raising the Curie temperature with increasing y, the dependence of Curie temperature on y in the case ofx=0.5 is shown in FIG. 4. As is evident from the figure, the Curie temperature becomes higher with increasing y. In other words, the temperature variation of the value of 41rMs with an increase in y has been outstandingly improved.

- Our experiment has demonstrated that an increase in' y causes higher Curie temperatures irrespective of the values of Marked improvements in the value of the linewidth (AH) with increasing ythat is, with larger Y O substitutions, can be also observed, as shown in FIG. 5

Referring to FIG. 5, curve a indicates the linewidth AH as a function of y for x=0.05. At first, AH decreases with an increase in y and reaches a minimum AH=180 at y=0.5. With a further increase in the value of y, AH begins to increase and reaches the compensation point at y=l .05, at which an abnormal phenomenon of AH can be observed. With a still further increase in y, AH decreases until it reaches a minimum at about y=l .8 and thereafter, increases again. In case y exceeds 2.4, the linewidth AH becomes degraded as compared with that fory=0 or that of the composition not substituted with Y O Curve b indicates AH as a function of y for x=0.5. At first, a decrease in AH occurs with increasing y, AH reaching an excellent value AH=53 at y=0.4. Thereafter AH begins to increase with an increase in y to reach the saturation point at y=l .5, at which point an abnormal phenomenon of AH can be observed. Thereafter AH begins to decrease again with increasing y, reaching a minimum AH=200 at y=2.0. Beyond the point y=2.4, the value of AH becomes larger than that of the composition not substituted with Y O for x=0.05, which is 290.

As will be evident from the foregoing description, an increase in y causes marked improvements not only in Curie temperature, but also in linewidth (AH).

FIG. 6 shows the dependence of 41rMs on y for x=0.5. The value of 41rMs decreases at first with increasing y and the composition at y=l.5 manifests the antiferromagnetic properties. Thereafter 41rMs increases with increasing y. As is evident, 41rMs can take any desired values less than 800 gauss with varying values of y. This is advantageous in employing the present materials in the VHF, UHF or SHF band range.

Conventional materials with low 41rMs values have been considered to be of little utility because of their low Curie temperatures, unfavorable temperature stability of 411Ms and high magnetic losses. Therefore, the Ca-V series garnets having low 41rMs, low linewidths, and high Curie temperatures prepared in accordance with to this invention are unprecedented heretofore. For instance, the indicated Ca-V garnet materials possess the excellent performance such as 41rMs=26O, AH=96, Curie temperature 228 C., for x=0.5 and y=l.0. The yttrium-iron-aluminum series garnets and magnesium-manganese series ferrites currently used as microwave device materials have been found inadequate for the following reasons: The Curie temperature approaches l00 C., for 4'n-Ms values of the order of 260 gauss, which causes an increase in the temperature variation of 41rMs and a drift of tuning points due to temperature variations. This results in a degradation in the isolation property, an increase in the VSWR, and an increase in the insertion loss.

As will be apparent, this invention can provide calciumvanadium series ferrimagnetic garnets with high Curie tem- TABLE 2 Curie Hinterlng terncondttlons All new 41 Ms (oertun: x y C. Hrs. (gauss) sheds) C.)

Sample No.:

Note.Sample numbers bearing an asterisk denote compositions mt menses isthqss sssmx iemYsst ys1.--.-.

The effectiveness of the present invention in causing a marked improvements in linewidth will be readily evident from an examination of AH values for various compositions as shown in table 2.

Thus, varying the values of x and ythat is, varying the amounts of Ge O and Y O substitutions, in the calciumvanadium series garnet compositions which can be expressed 3-1I v}[ 2]( l.50.5.r+0.5u .t l.5-0.5.r0.5|I) l2 enables high Curie temperatures and low linewidth (AH) values which are much lower than the values of AH of the unsubstituted calcium vanadium garnet compositions.

The x and y values in the compositions of this invention lie, as mentioned previously, within the polygonal area A-B-C- D-E shown in FIG. 7 which is bounded by the lines connecting t sqqtd natss;

From the area A-BC-D-E, the range of 0.95 S y-x a 1.05 should be excluded, as mentioned previously. The reason why the area A-B-C-D-E is defined is as follows:

The compositions outside the lines A-B and E-A manifest to an insufficient degree the beneficial effects of this invention to render them useful in practical applications; the compositions lying in the area above the line B-C possess low Curie temperatures less than- 100C. and large temperature variations of 41rMs, rendering them difficult for practical use, although they have improved AH values; the compositions lying outside of the line CD and having relatively small values of y possess low Curie temperatures and large temperature variations of 41rMs; in the compositions outside the line C-D and having a larger value for y, AH values are not substantially improved; the compositions lying outside of .the line D-E have high Curie temperatures, but their AH values are substantially the same as or a little inferior to the AH value of the unsubstituted Ca-V garnet compositions. In order to improve the AH values of compositions with y values larger than those of the compositions of the instant invention. sintering for long time intervals at extremely elevated temperatures would be necessary, which apparently does not meet the objects of this invention.

Now the effect of Ta-substitution combined with Geand Y- substitutions will be clarified with reference to FIGS. 8 to 13.

Samples hereinafter referred to which are expressed as and have the values ofx= 1.0,y= 0 z l.6,andz= 0 0.4 were produced and measured in the same manner as'used for the compositions of table 1. Referring to FIG. 8 illustrating the dependence of z(Ta) on AH where x=0.4 and y=0.4, the value of AH which is 148 at z=0 gradually decreases with increasing reaching a minimum AH=76 at z=0.l. Further substitution of Ta causes AH to increase. In excess of z=0.l7, the value of AH becomes equal to that at z=0. Further increase in z(Ta) causes an increase in AH, or deterioration of AH, beyond the initial value until the point z=0.25 has been reached at which the 16a and 24d site unbalance in the number of Fe-ions disappears and ferrimagnetism is lost. As a result, the value of AH becomes extremely high. As the value of z increases, such as to 0.3 or 0.4,the value ofA H decreases accordingly. 74W 7 FIG. 9 indicates the influence of 2 (Ta) on the value of 4-rrMs where x and y are both 0.4. An increase in the amount of substitution of Ta causes a decrease in 41rMs and the value of 4rrMs becomes extremely low at z=0.25 at which the 16a and 24d site unbalance disappears. The increased substitution, such as to values of z=0.3 or 0.4, causes an increase in 41rMs again.

The manner in which the Curie temperature decreases with an increase in z (Ta) is shown in table 3.

As heretofore mentioned, substitution by Ta causes a decrease in 41rMs in spite of its small amounts. Notably in the range z=0 0. l 7, the substitution is also effective for lowering the value of AH. As z=0.l7 is exceeded, however, AH becomes higher than its initial value at z=0, while for large values of z the Curie temperature becomes low. Therefore, the effective z range is the 0 2 s 0.17. Since substitution effect is limited for values of 2 less than 0.02, the preferable 1 range is 0.02 s z s 0.l7.

FIG. 10 indicates the influence of x (Ge) on AH in the composition where y=0.4 andz=0. l. The value of AH, which is 220 at x=0, decreases with an increase in x and reaches 25 at x=0.8.

H6. 11 shows the dependence of 41rMs on x in the same case. The value of 41rMs increases with increasing x, becoming more than 600 gauss at x=0.8.

Changes in Curie temperature in this case are listed in table 4. it will be seen that the Curie temperature decreases with increasing x and becomes lower than l50 C. for values of x in excess of x=0.8, resulting in an increase in the temperature variation of 41rMs. Therefore, the effective x values are in the range 0.05 s x 5 0.8. Since substitution effect is limited for values of x==0.l as is apparent from FIG. 10, the range of x values is preferably 0.] a x s 0.8.

TABLE 4 x z Curie temp. ('C.)

0 0.4 0.] 13. 0.2 0. [I III 0.4 0.4 0.] I 0.6 0.4 0.] I: 0.8 0.4 0.] I51 [.0 0.4 0.] l'l FIG. 12 indicates the influence of y (Y) on AH in the cases of x=0.4 and z=0.l (curve a) and x=0.6 and z=0.l (curve b). The value of AH at y=0 for the curve a is 139 and an increase in y causes a decrease in AH, the value reaching 50 at y=0.2. Then, the value of AH increases with an increase in y and, at y=l.0, the relative 16a and 24d site unbalance in the Fe-ion number disappears and an abnormal phenomenon of AH occurs. Thenceforth a decrease in AH occurs again with an increase in y, reaching AH=l l0 at y=l.4. At y=l .6, the value of AH begins to increase. This is because the sintering temperature becomes higher according as the quantity of yttrium substitution is increased.

In case of curve b, the value of AH, which is 75 at y=0. begins to decrease with an increase in y, reaching 39 at y==0.2. Thereafter the value of AH begins to increase with increasing y. At y==l.2, the and 24d site unbalance disappears, at which point the value of Abecomes exceedingly high. Thenceforth the value of AH decreases gradually with an increase in y.

FIG. 13 illustrates the dependence of 41rMs on the value of y in the same case. With an increase in y, i.e., yttrium substitution quantities, the value of 41rMs decreases. In case of x=0.4 and z=0.l (curve a), the 160 and 24d site unbalance occurs at y=l.0, while in case of x=0.6 and z=0.l (curve b), at y=l.2. Under this situation, the 411Ms value becomes less than 50. This point corresponds to approximately the point where the relation 4z+yFl is satisfied. It is generally considered that compositions meeting this relationship manifest antiferromagnetism and do not manifest ferrimagnetism.

The Curie temperatures increase with an increase in y as shown in table 5 and this increase tends to compensate for a decrease in Curie temperature caused by the combined tantalumand germanium-substitutions. An increase in y causes higher Curie temperatures as is evidenced by the fact that a value of C. in case of x=0.4z=0.l and y=4) increases to 258 C. in case of x=0.4, z=0.l, and y=l.4, and the improved '41rMs versus temperature characteristic. But an increase in y is disadvantageous in the use of large quantities of Y,O which is an expensive raw material. This inevitably renders finished material costs expensive. Furthen'nore, large yttrium substitutions call for higher sintering temperatures, which are not suited to large-scale industrial production. On the other hand, values of y less than 0.05 manifest little of the yttrium substitution effect of yttrium. Therefore the effective range of y is determinedas0.05 i y s 1.4.

Thus, with the tantalum-, germaniumand yttrium-sub stituted calcium-vanadium series garnet materials, excellent AH values, low 41rMs, high Curie temperatures and a low cost can be realized. Also, better 41rMs versus temperature characteristics than the aluminum-substituted YIG is obtained as are evident from FIG. 1. For instance, the Curie temperature of the aluminum-substituted YlG indicated by YlG (Al) in the figure which have a 41rMs value of about 350 gauss at room temperature is at or near 120 C., and hence the temperature variation of 41rMs is quite large. One of the compositions of this invention which is indicated by curve No. V in FIG. 1 possesses a 41rMS value at room temperature of 365 gauss and Curie temperature of 209 C. at which 41rMs becomes 0. The 41rMs versus temperature characteristics of this composition are quite superior to those of the aluminum-substituted YlG.

As has been mentioned, the Ca-V series ferromagnetic garnets according to this invention offer advantages over the known yttrium-iron-aluminum garnets series of lw-41rMs microwave magnetic materials such as lower magnetic losses, higher Curie temperatures, improved 41rMs versus temperal0 D-E shown in FIG. 7 of the drawing which is bounded by the ture characteristics, lower costs which comes from the use of smaller quantities of yttrium, and also lower sintering temperatures (of the order of as low as 200 C.) than those of the aluminum-substituted YlG, which advantages can be important in large-scale industrial production.

The compositions of the invention provide inexpensive microwave element materials forum in VHF, UHF'and SHF band ranges, the materials having low 41rMs values, improved 41rMs versus temperature characteristics, low magnetic losses and being also easily amendable to large-scale production.

The tantalum-germanium-yttrium substituted calcium-vanadium garnet compositions are particularly useful in this regard as follows:

lines connecting the coordinates:

C 1 .8 l I D 0.5 2.4 E 0.05 2.4

and wherein the range expressed by the relation 0.95 5 y-x s 1 .05 is excluded from said area.

2. Calcium-vanadium ferrimagnetic garnets having compositions expressed by the formula: {C .'1u y}[ 2 z z] (F !.5 0.5.z+0.5y+z .r j.5-0.5.r 0.5|1:z) 12 h ein va uss flz y and .1110? n the 3112S2Pf as 0.5 g x; 0.8; 0.05 y 1.4 and 0 z E 0.17, respectively, but excluding the values of x, y and 1 determined by re stiwfifiijfir E .9 2......

3. Calcium-vanadium series ferrimagnetic garnets as claimed in claim 2, wherein the values of x, y and z are in the ranges of 0.15 x 0.8; 0.05 y 5 1.4 and 0.02 i z 5 1.7, respectively, but excluding the values of x, y and z detennined by the relation 0.8 4z+yx 1.2. 

2. Calcium-vanadium ferrimagnetic garnets having compositions expressed by the formula: Ca3 yYy (Fe2 zTaz)(Fe1.5 0.5x 0.5y zGexV1.5 0.5x 0.5y z)O12 wherein values of x, y and z are in the ranges expressed as 0.05 < or = x < or = 0.08; 0.05 < or = y < or = 1.4 and 0<z < or = 0.17, respectively, but excluding the values of x, y and z determined by the relation 0.95 < or = 4z+y-x < or = 1.05.
 3. Calcium-vanadium series ferrimagnetic garnets as claimed in claim 2, wherein the values of x, y and z are in the ranges of 0.1 < or = x < or = 0.8; 0.05 < or = y < or = 1.4 and 0.02 < or = z < or = 1.7, respectively, but excluding the values of x, y and z determined by the relation 0.8 < or = 4z+y-x < or = 1.2. 